Cross-Model Validation of Coronagraphic Exposure Time Calculators for the Habitable Worlds Observatory: A Report from the Exoplanet Science Yield sub-Working Group

TL;DR

This study compares three coronagraphic exposure time calculators for the Habitable Worlds Observatory, revealing significant discrepancies and identifying causes to improve their consistency for better mission planning accuracy.

Contribution

It provides the first systematic cross-model validation of ETCs, highlighting differences and proposing pathways for harmonization in exoplanet observation planning.

Findings

ETCs vary by about 60% in exposure time estimates

Discrepancies stem from differing methods, assumptions, and inputs

Addressing flagged issues could reduce differences to below 30%

Abstract

Estimating the exoplanet scientific productivity of the Habitable Worlds Observatory requires estimating science exposure times. From exoplanet yields to spectral retrievals, exposure times are at the heart of our understanding of the capabilities of this future mission. As such, ensuring accuracy and consistency between different exposure time calculators (ETCs) is critical. We summarize the efforts of the Exoplanet Science Yield sub-Working Group's ETC Calibration Task Group, which conducted a calibration study from March 4 to June 30 of 2024. We compare three commonly-used coronagraphic exposure time calculators. We find that the ETCs use a broad variety of differing methods, assumptions, and inputs that produce variation in the final exposure times at the ~60% level. The causes for the disagreement have largely been identified, flagged for further development efforts, and in some cases retired since the conclusion of this effort. We expect that addressing the flagged efforts will bring the ETCs to within better than ~30% agreement.